Electrophotographic developing device using liquid

ABSTRACT

Various structures are disclosed for producing a layer of liquid developer to cover the visible portion of an edge mounted section of an electrophotographic recording medium without wetting the mount beyond the edges bordering said visible portion. During application of the developer to said visible portion there is no relative movement of the developer device across the surface of the visible portion.

United States Patent 1191 Saito et a1.

ELECTROPHOTOGRAPHIC DEVELOPING DEVICE USING LIQUID Inventors: TakashiSaito; Shusei Tsukada, both of Tokyo, Japan Canon Kabushiki Kaisha,Tokyo, Japan Filed: Sept. 30, 1970 Appl. No.: 76,729

Assignee:

Foreign Application Priority Data 001. 11, 1969 Japan ..44/81378 us. 01...118/637, 95/89 R, 117/37 EE, 118/DIG. 23

1111.01. ..G03g 13/00 Field of Search ..1 18/637 LX, 637, 118/D1G. 23;117/37 LX; 95/89 References Cited UNITED STATES PATENTS Hakanson ..118/637 Nail .1 ....118/637 Lehmann Tyler et a1. ..95/94 51 Apr. 17, 1973Crawford, Developing Electrostatic Charge Patterns, Vol. 8, No. 4, Sept.65, IBM Technical Disclosure Bulletin.

Primary Examiner-Mervin Stein Assistant Examiner-Leo MillsteinAttorney-Watson, Leavenworth & Kelton ABSTRACT Various structures aredisclosed for producing a layer of liquid developer to cover the visibleportion of an edge mounted section of an electrophotographic recordingmedium without wetting the mount beyond the edges bordering said visibleportion. During application of the developer to said visible portionthere is no relative movement of the developer device across the surfaceof the visible portion.

7 Claims, 14 Drawing Figures PATENTEDAPR 1 11915 3.127; 578

SHEET 1 UF 5 PATENTEB APR 1 7 I973 SHEET 2 OF 5 FIG. 4

90 W A. M 4 & M. ll

FIG. 5

PATENTEB APR 1 71975 SHEET t 0F 5 FIG. 8b

FIG. 9

PATENTED APR 1 7 I975 SHEET S [1F 5 FIG. |o

FIG. II

FIG. I2

ELECTROPHOTOGRAPHIC DEVELOPING DEVICE USING LIQUID BACKGROUND OF THEINVENTION 1. Field of the Invention This invention generally relates toan electrophotographic developing device using liquid, and moreparticularly to such a developing device in which an electrophotographicfilm comprising a recording medium securely held in an apertured supportframe by means of an adhesive agent can be developed by developingsolution without the support frame, and the adhesive agent beingmoistened by the developing solution, whereby the support frame and theadhesive agent is protected against any stain or injury imparted by thedeveloping solution.

2. Description of the Prior Art Electrophotographic film is well known,e.g., the film used with a microfilmer, projector or the like, and thereare various types of such film. Electrophotographic film generallycomprises a thin layer of photoconductive material disposed on asubstrate treated for electrical conduction. Various organic orinorganic com-- pounds are known as suitable for such photoconductivematerial. Although inorganic compounds are effective for use as thephotoconductive material, organic compounds are more effective and atransparent photoconductive medium provided by such photoconductivecompounds applied onto a transparent substrate is very suitable for usewith a microfilmer, projector or the like.

It is also known that the organic photoconductive compounds includepolycyclic aromatic compounds such as anthracene, pyrene, etc.,heterocyclic compounds such as imidazole, oxazole, thiazole, triazole,carbazole, etc., or high molecular substances such as polyvinylcarbazole, polyvinyl acenaphthene, etc. By applying thesephotoconductive materials onto a transparent substrate of polyester,polystyrene, polyvinyl chloride, triacetate fiber or the like, there areprovided transparent photosensitive mediums. These photosensitivemediums may be subjected to known electrophotography including thevarious steps of electric charging, exposure, development and fixing,whereby electrostatic latent images are formed and developed on thephotosensitive mediums. The photosensitive mediums or films now havingvisible images thereon are then held by holders or mounts to form slidesor microfilm cards which may be used as recording mediums. Theserecording mediums are thus ready for use with projectors or similarmachines.

According to the described system of the prior art, however, theproduction of a visible image on the photosensitive films precedes themounting thereof on the mounts or holders, and during the mountingprocess the visible images formed on the photosensitive films may beinjured inadvertently or otherwise. To eliminate such disadvantage, itwill occur to mind that fresh photosensitive films having no imageformed thereon should first be mounted in holders or mounts and thensubjected to the described various electrophotographic steps for theformation and development of electrostatic latent images, wherebycomplete and flawless photosensitive films in the form of slides will beprovided for use with projectors or the like.

However, photosensitive films supported by mounts or holders mayencounter various difficulties when they are subjected to knownelectrophotographic image reproducing processes. As known, developmentusing liquid is preferred in the electrophotographic processes, or morespecifically in the developing process, and it is in this process that agreat problem occurs. In general, development using liquid hasheretofore been accomplished by immersing the recording medium indeveloping solution, or by causing the developing solution to fiowthrough a gap between the surface of the recording medium to bedeveloped and a plate disposed in opposed relationship with thatsurface, or by blowing the developing liquid against the surface to bedeveloped. Each of these methods has its own features, and is effectivewhen applied to the films without mounts. However, none of these methodsare suitable to develop through the aperture formed in the support framethe electrophotographic film of the type used with the present inventionwhich is held in the previously described support frame, because thesupport frame around the aperture is exposed to the developing solutionand moistened thereby. Such moistening of the frame or mount on the onehand increases the rate of consumption of the developing solution and onthe other hand requires a longer time for drying and also causes stainsor blots or other undesirable injuries to be produced on the supportframe.

SUMMARY OF THE PRESENT INVENTION It is a primary object of the presentinvention to provide an improved developing device using liquid whichcan developa photosensitive film held by a support frame such as aholder, mount or the like without moistening the support frame.

It is another object of the present invention to provide an improveddeveloping device using liquid which ensures developing solutioncontacting only the film surface of the photosensitive film of thedescribed type when it is subjected to the developing process.

It is still another object of the present invention to provide animproved developing device using liquid which ensures developingsolution rising or swelling in a shape corresponding to the desiredsurface to be developed of the photosensitive film of the describedtype.

It is yet another object of the present invention to provide an improveddeveloping device which ensures developing solution rising or swellingin a shape corresponding to the desired surface to be developed of thephotosensitive film of the described type so as to provide fine mobilityof the developing solution.

According to the present invention, in order to develop through theaperture formed in the support frame an electrostatic latent imageformed on a photosensitive film held in said support frame, developingsolution is caused to rise or swell in a shape corresponding to thesurface area of the film carrying the latent image so as to contact thatsurface, whereby the developing solution positively develops the latentimage while it is given a fine mobility to maintain itself effective forthe purpose of development.

The invention will be described in detail hereunder with respect tovarious embodiments thereof shown in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showingthe developing device according to a first embodiment of the presentinvention.

FIG. 2 is a vertical cross section of the device of FIG. 1 showing themanner in which developing solution is caused to flow up through thesmall holes in the upper end of the developing box and rise or swellover the developing box.

FIG. 3 is a fragmentary sectional view of the same device showing themanner in which the rising developing solution contacts theimage-carrier surface of a recording medium.

FIG. 4 is a vertical cross-sectional view showing the developing deviceof FIG. 1 as incorporated in an electrophotographic slide printer.

FIG. 5 shows, in perspective view, a second form of the presentinvention together with a recording medium used therewith.

FIG. 6 shows, in cross section, the developing device of FIG. 5 forillustrating the manner in which developing solution is fed upwardlythrough a plurality of discrete cylinders facing the surface to bedeveloped so as to rise and contact that surface.

FIG. 7 is a fragmentary sectional view showing the interior shape of thecylinders shown in FIG. 6.

FIGS. 8(a) to 8(a) are cross-sectional views showing a third form of thepresent invention and illustrating the manner in which developingsolution filling the developing box rises or swells through the open topof the box due to its own surface tension and contacts the surface to bedeveloped.

FIG. 9 shows, in cross section, the developing device of FIG. 8 asincorporated in an electrophotographic slide printer.

FIG. 10 is a cross-sectional view showing a fourth embodiment of thepresent invention.

FIG. 11 is a similar view showing the manner in which the recordingmedium is developed by the device of FIG. 10.

FIG. 12 shows, in cross section, a fifth embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 3,there is shown a first embodiment of the present invention used with aknown recording medium 1 held at its edges by a support frame or mount2. The recording medium 1 has all but its peripheral edges exposed orvisible in an aperture a bounded by the inner side edges of the supportframe 2. The shown developing device of the present invention comprisesa developing box 3 having an open top a, which is dimensioned somewhatsmaller than the area of the recording medium 1 defined by'the aperturedwalls of the support frame 2, for a reason described later. A plate 5formed with a number of small holes is fitted in the open top a of thedeveloping box 3 for a certain purpose to be described. The developingbox 3 is filled with developing solution 4 which is introduced thereintofrom an unshown supply source through a supply pipe 6 in communicationwith a pump or like pressure source (not shown).

The developing solution 4 introduced into the developing box 3 is fedupwardly along the inner side wall surfaces of the box (FIG. 2), andfurther fed out of the developing box 3 through the holes in the plate 5so that the out-flow of the developing liquid 4 may form a layer ofliquid which is to contact the effective area of the recording medium 1carrying an electrostatic latent image thereon (FIG. 3).

Whenthe upper surface of the liquid layer formed over the upper openinga of the developing box 3 contacts the latent image on the recordingmedium 1, the contact pressure between the developing liquid and thesurface of the recording medium as well as the surface tension of thedeveloping liquid causes the liquid forming the layer to flow laterallytoward the inner side edges of the support frame 2 to sweep the entireeffective surface area of the recording medium 1, whereafter thedeveloping solution 4 flows downwardly along the vertical inner sideedges of the support frame 2. Thus, the developing solution 4 developsthe entire latent image on the recording medium 1 without moistening thesurrounding support frame 2. The overflow of the developing solution isreceived in a sump 7 disposed around the developing box 3 in the lowerportion thereof.

- To attain such a flow effect of the developing solution 4 as shown inFIG. 3, the top opening a of the developing box 3 is dimensioned smallerthan the apparentv area of the recording medium 1 defined by theapertured walls of the support frame 2 as shown in FIG. 3, although thedimensions of the opening a are actually determined by various factorssuch as the viscosity and supply rate of the developing solution,wettability of the recording medium, spacing between the open top a ofthe developing box 3 and the lower surface of the recording medium 1,etc.

According to experiments, the layer of the.develop- 'ing solution 4formed over the open top a of the developing box 3 may preferably have athickness of the order of l to 3 mm. as measured from the surface ofthat open top a, and such thickness is the most stable and appropriateto achieve the intended effect.

The plate 5 having a number of small holes and fitted I in the open topa of the developing box 3 serves to stabilize the out-flow of thedeveloping solution as well as acts as a developing electrode. Ifdesired, a wire screen may be employed instead of the apertured plate 5.

FIG. 4 shows the described embodiment of the present inventionincorporated as a developing device in an electrophotographic printerfor the formation of slides.- In the illustrated printer, the recordingmedium 1, such as an electrophotographic film supported by the supportframe or slide mount 2, is secured to a holder 8 by suction means or thelike (not shown). Below the film 1, a process bench 12 including anelectrical charging means 9, photoexposure shutter 10 and developingdevice of FIG. 1 generally indicated by 1 l is arranged to movehorizontally in the direction in-- dicated by the straight arrow, sothat the film 1 is electrically charged and exposed to image-carrierlight to form an electrostatic latent image, and is then developed bythe developing device 11. Reference numerals 13 and 14 designate aprojection lens and shield plates, respectively.

During the developing process, the developing solution 4 supplied thedeveloping box 3 by means of pump 15 is fed upwardly to pass through thetop opening a of the box 3 so as to contact the electrostatic latent"image formed on the film l, in the manner described above. Thus, thelatent image is rendered visible without the support frame or slidemount 2 being wetted by the developing solution. As shown, the sump 7may have its wall 7 sufficiently tall to permit the upper end thereof tointimately contact the lower surface of the slide mount 2, whereby theslide mount 2 can be perfectly shielded from the overflow of thedeveloping solution. The developing solution suitable for theelectrostatic latent image formed on the film 1 in this case should becomposed of toner particles having diameters in the range of 0.5 to 5 p.and dispersed in an insulating liquid.

Referring to FIGS. 5 and 6, there is shown another form of the presentinvention, which employs a plurality of closely spaced, discretecylinders projecting upwardly from the upper end of a cylindricaldeveloping box 16 having a supply pipe 17 connected thereto. Thecylinders or nozzles 15 are arranged to have the developing solution 4pass therethrough toward the recording medium 1 in the manner shown inFIG. 6. In this case, the developing solution 4 flows upwardly througheach of the discrete cylinders 15 to reach the image-carrier surface ofthe recording medium 1 while also flowing laterally toward the innerside edgesof the support frame 2, whereafter' the overflow flowsdownwardly along the vertical channels defined by the outer wallsurfaces of adjacent cylinders 15 and returns into the developing box16.

With this arrangement, the flow pattern of the developing solution 4 issuch that the part of the solution 4 flowing up through each discretecylinder 15 forms a discrete upward stream, which sweeps theimage-carrier surface of the recording medium 1 and then flows down intothe channels between adjacent cylinders 15. In this flow pattern, thetendency of the developing solution 4 to flow excessively toward theinner side edges of the support frame 2 is effectively reduced duringthe developing process, so that the outflow pressure and surface tensionof the liquid are stably balanced with each other to thereby strictlylimit the area ofthe recording medium contacted by the developingsolution and accordingly perfectly'protect the support frame 2 againstmoistening.

As will be appreciated from the foregoing, the embodiment now underdiscussion achieves protection of the support frame 2 better than thefirst-described embodiment in which part of the developing liquid 4flowing through the open top a of the developing box 3 may go beyond theinner side edges of the support frame 2 due to an increased liquidpressure to thereby reach and moisten the lower side thereof.

To provide such an ideal flow pattern as shown in FIG. 6, it isdesirable in fact that suitable considerations be given to variousfactors such as the flow rate of the developing solution, width of thechannels between cylinders 15, dimensional relationship between theimage-carrier surface and the swollen liquid surface, shape of theindividual swollen liquid portions, etc.

The cylinders 15 for passing the developing solution therethrough mayhave a generally circular, square or other suitable cross section. Thebore of each cylinder 15 may be enlarged as shown in FIG. 7, so that thepressure imparted from the developing solution to the image-carriersurface of the recording medium may be reduced so as to ensuresatisfactory development to be achieved. It may also be possible toprovide a screen on the cylinders 15 thereacross to thereby stabilizethe out-flow of the developing liquid. Such a screen or the portion ofthe cylinders 15 which is adjacent to the surface to be developed mayfurther serve as a developing electrode if it is formed of anelectrically conductive material, and in such cases a bias voltage maybe applied if required.

Further, in case where the latent image to be developed has a relativelyhigh residual potential or where members such as cylinders 15 facing theimagecarrier surface have a non-uniform surface, these members shouldeffectively be formed of an electrically insulating material so as toattain a uniform developing effect.

FIGS. 8a, 8b, and show a further form of the present invention, in whichthe developing box indicated by 18 is in the form of a dish or containerhaving an open top a, which is again dimensioned smaller than the areaof the recording medium 1 defined by the inner side edges of theapertured support frame 2. The developing solution 4 filling thedeveloping box 18 is caused to rise or swell through the open top a dueto its own surface tension (FIG. 8a), and the surface of the recordingmedium 1 carrying an electrostatic latent image thereon is brought intocontact with the surface of the swollen liquid 4 to thereby cause theliquid to expand laterally toward the inner side edges of the supportframe 2 while keeping contact with the image-can rier surface, of therecording medium, whereafter the liquid flows down. along the verticalinner side edges of the support frame 2 due to its gravity (FIGS. 8b).

With this arrangement, the balance between the surface tension andgravity of the developing solution 4 as well as the wettability of therecording medium 1 serves to prevent any of the liquid 4 from fallingout of the developing box 18, and thus the entire latent image can bedeveloped without any over-flow of the developing solution. FIG. 8cshows the developed recording medium as it is moved away from thedeveloping liquid.

FIG. 9 illustrates the developing device of FIG. 8a incorporated in anelectrophotographic printer for the formation of slides. As shown, therecording medium such as a transparent film 1 formed of organicsemiconductorand supported by the support frame or slide mount 2 is setin an opening b formed in a holder 20 rotatable about a shaft 19, theopening b being larger than but proportional to the aperture a of theslide mount 2. By rotating the holder 20, the film 1 held there in ispassed through electrical charging means (not shown) and exposure device21 to form an electrostatic image on the film l, which is subsequentlypositioned above the developing device 22 as shown, whereby the latentimage is made visible.

The developing device 22 has a pipe 23 for supplying therethrough thedeveloping solution 4 from an unshown supply source into a tank 24 forstoring the supplied liquid. Within the tank 24 there is disposed adeveloping box 25 having a high resistance to the developing solution.The developing box 25 shown in FIG. 9 corresponds to that indicated by18 in FIG. 8a, and it is securely mounted on a support plate 28 which isvertically movable with the aid of spring 26 and wire means 27. Thesupport plate 28 slides along vertical guide posts 29.

The developing box is normally urged downwardly by the wire means 27 andsubmerged in the developing solution 4 contained in the tank 24, butwhen the film 1 having an electrostatic latent image formed thereon ispositioned above the developing box 25, the wire means 27 is released toallow the spring 26 to upwardly bias the support plate 28 and thedeveloping box 25 together. When the open top a of the developing box 25appears above the liquid surface in the tank 24, the quantity of liquidfilling the box 25 rises or swells upwardly above the open top a of thebox 25 due to its surface tension to form a convex meniscus. Avertically adjustable stop member is provided on each post 29 adjacentthe top thereof so as to stop the upwardly moving box 25 at such a levelthat the surface of the swollen liquid contacts the image carriersurface of the film 1 so as to develop the electrostatic latent imagethereon.

Where the aperture a formed in the slide mount 2 holding the film l isdimensioned 24 X mm. as is usual, the standard dimensions for theopening a of the developing box 25 are in the range of 20 .to 21 mm. X31 to 32 mm., provided that the developing solution in use is composedof toner particles dispersed in kerosene. The depth of the box 25 may besuitably determined by the density of the developing solution and thetime required for the development.

After the development is completed, the support plate 28 may be lowered,slowly at first, and then faster, whereby the developing solution in thetank 24 is stirred and maintained at a uniform density.

Referring to FIG. 10, there is shown a further form of the developingdevice embodying the present invention. In this alternative embodiment,a relatively nar-, row vertical flow passage 31 having a flange-likedeveloping plate 32 formed integrally therewith is disposed with itsopen top facing the center portion of therecording medium 1 similar tothat shown and described in each of the preceding embodiments. Thedeveloping plate 32 is substantially parallel to the recording medium 1and its outer edges lie inwardly of the inner side edges of the supportframe 2 holding the recording medium 1, as in the cases of the previousexamples. Thus, the developing solution 4 is fed upwardly through thepassage 31 toward the center area of the recording medium, and theout-flow of the liquid then flows laterally along the developing plate32 toward the inner side edges of the support frame 2, from which theliquid flows downwardly.

As soon as the image-carrier surface of the recording medium 1 contactsthe top of the rising or swollen liquid 4, the liquid is caused to flowlaterally through the gap between the image-carrier surface and thedeveloping plate 32 and reach the inner side edges of the support frame2 due to the surface tension, as already described with respect to FIG.2, while sweeping the entire area of the image-carrier surface.Thereafter, the liquid is directed downwardly by the inner side edges ofthe support frame 2 and flows down along the outeredges of' the plate 32and outer side wall surface of the passage 31. In this way, developmentof the recording medium 1 can be accomplished without the support frame2being wet.

To achieve the ideal flow pattern as shown in FIG. 11, the size of thedeveloping plate 32 relative to the image-carrier surface should bedetermined by such factors as the viscosity of the developing solution,wettability of the recording medium and so on.

Finally, FIG. 12 illustrates still another form of the presentinvention. As shown, a layer of sponge-like material 33 is disposed overthe open top of a developing box 34, the layer 33 being dimensionedsmaller than the area of the recording medium 1 which is defined by theinner side edges of the support frame 2. A supply pipe 35 is connectedto the developing box 34 to supply developing solution 4 thereinto withthe aid of a pump or other pressure source (not shown). The developingsolution 4 introduced into the box 34 flows upwardly to permeate throughthe sponge and form a thin layer of liquid over the layer of sponge 33.Such a thin layer of liquid is always defined within a predeterminedarea, and this in turn means that development is also effected within apredetermined area of the recording medium 1.

The present invention has been shown and described with respect to thecases where a photosensitized filmv held by a support frame is developedwithout the. support frame being moistened by the developing solution,whereas it will be apparent to those skilled in the art that thedeveloping device of the present invention can be' highly effectivelyapplicable in cases where only a part of -a sheet-like photosensitizedfilm carrying a number of'latent images thereon is to be developed.

' As has been disclosed above, the developing device of the presentinvention utilizes the surface tension, gravity and injection force ofthe developing solution to thereby form a predetermined pattern of riseor swell of the liquid in opposed relationship with a surface to bedeveloped, whereby development is constrained to take place only withina desired area of that surface. Also, the shape of the rising or swollenliquid is so varied as to eliminate any sharp collision thereof againstthe surface to be developed, as well as to provide fine mobility of theliquid with respect to that surface, whereby the developing liquid ismaintained at a constant toner density which results in a highlyexcellent image reproducing effect.

, What is claimed is:

1. A developing device for developing an electrophotographic image on asection of electrophotographic photosensitive film within an aperture ina mount holding said film, said device comprising in.

combination means for supporting said mounted film at a liquiddeveloping station and means for forming and contacting theimage-carrier side of said film within said aperture with a layer ofelectrophotographic liquid developer having a surface configurationprior to contact with said film which is substantially similar to butsufficiently smaller in area than said aperture to allow for spreadingof saiddeveloper up to but not beyond the borders of said aperture as aresult of the filmwetting characteristics of said developer to therebydevelop an area coextensive with said aperture without wetting more ofsaid mount than the inner side edges thereof bordering said aperture.

2. A developing device according to claim 1, wherein said means forapplying developer comprises a flat perforated plate element having ashape and size similar to but slightly smaller than said aperture, meansfor positioning said plate element parallel to and closely spaced fromsaid film, and means for feeding said developer through said plateelement to produce a layer of developer bridging the space between saidplate element and said film.

3. A developing device according to claim 1, wherein said means forapplying developer comprises an array of nozzles disposed side-by-sidein closely adjacent spaced relationship, said nozzles terminating in aplane parallel to and closely spaced from said film, said array having ashape and size similar to but slightly smaller than said aperture, andmeans for feeding said developer through said nozzles to produce a layerof developer beyond said nozzles bridging the space between said planeand said film.

4. A developing device according to claim 3, wherein each of saidnozzles terminates in an enlarged passage for reducing the pressureunder which said developer is applied to said film.

5. A developing device according to claim 1, wherein said means forapplying developer comprises a container for a quantity of saiddeveloper having an open top of a shape and size similar to but slightlysmaller than said aperture, means for filling said container to itsmaximum capacity to form a convex meniscus of said developer, and meansfor moving said container towards the surface of said film until saidconvex meniscus of said developer bridges the space between said top ofthe container and said film.

6. A developing device according to claim 1, wherein said means forapplying developer comprises a flat plate element having a shape andsize similar to but slightly smaller than said aperture, means forpositioning said plate element parallel to and closely spaced from saidfilm, and means for feeding said developer through said plate element atthe center thereof to produce a layer of developer over said plateelement bridging the space between said plate element and said film.

7. A developing device according claim 1, wherein said means forapplying developer comprises a layer of sponge-like material having ashape and size similar to but slightly smaller than said aperture, meansfor positioning said layer of material parallel to and closely spacedfrom said film, and means for feeding said developer through saidmaterial to produce a layer of developer over the surface of saidmaterial bridging the space between said material and said film.

1. A developing device for developing an electrophotographic image on asection of electrophotographic photosensitive film within an aperture ina mount holding said film, said device comprising in combination meansfor supporting said mounted film at a liquid developing station andmeans for forming and contacting the image-carrier side of said filmwithin said aperture with a layer of electrophotographic liquiddeveloper having a surface configuration prior to contact with said filmwhich is substantially similar to but sufficiently smaller in area thansaid aperture to allow for spreading of said developer up to but notbeyond the borders of said aperture as a result of the film-wettingcharacteristics of said developer to thereby develop an area coextensivewith said aperture without wetting more of said mount than the innerside edges thereof bordering said aperture.
 2. A developing deviceaccording to claim 1, wherein said means for applying developercomprises a flat perforated plate element having a shape and sizesimilar to but slightly smaller than said aperture, means forpositioning said plate element parallel to and closely spaced from saidfilm, and means for feeding said developer through said plate element toproduce a layer of developer bridging the space between said plateelement and said film.
 3. A developing device according to claim 1,wherein said means for applying developer comprises an array of nozzlesdisposed side-by-side in closely adjacent spaced relationship, saidnozzles terminating in a plane parallel to and closely spaced from saidfilm, said array having a shape and size similar to but slightly smallerthan said aperture, and means for feeding said developer through saidnozzles to produce a layer of developer beyond said nozzles bridging thespace between said plane and said film.
 4. A developing device accordingto claim 3, wherein each of said nozzles terminates in an enlargedpassage for reducing the pressure under which said developer is appliedto said film.
 5. A developing device according to claim 1, wherein saidmeans for applying developer comprises a container for a quantity ofsaid developer having an open top of a shape and size similar to butslightly smaller than said aperture, means for filling said container toits maximum capacity to form a convex meniscus of said developer, andmeans for moving said container towards the surface of said film untilsaid convex meniscus of said developer bridges the space between saidtop of the container and said film.
 6. A developing device according toclaim 1, wherein said means for applying developer comprises a flatplate element having a shape and size similar to but slightly smallerthan said aperture, means for positioning said plate element parallel toand closely spaced from said film, and means for feeding said developerthrough said plate element at the center thereof to produce a layer ofdeveloper over said plate element bridging the space between said plateelement and said film.
 7. A developing device according claim 1, whereinsaid means for applying developer comprises a layer of sponge-likematerial having a shape and size similar to but slightly smaller thansaid aperture, means for positioning said layer of material parallel toand closely spaced from said film, and means for feeding said developerthrough said material to produce a layer of developer over the surfaceof said material bridging the space between said material and said film.